T2 has too big Rdson
The RDSon of T2 (BST82) which is used to switch on 50 ohm termination of trigger input is too big, resulting in too high input impedance. Replace with a low RDSon type (for example BSH103 used in the SPEC).
The RDSon of T2 (BST82) which is used to switch on 50 ohm termination of trigger input is too big, resulting in too high input impedance. Replace with a low RDSon type (for example BSH103 used in the SPEC).